The New York Times (Dec 4, 2015)
"At a news conference in San Bernardino,
David Bowdich, the F.B.I. assistant director in charge of the Los Angeles office, said he was aware of the post, which was taken down by Facebook on Wednesday, but he would not elaborate." (added emphasis)
The Los Angeles Times (Dec 6, 2015)
"Tashfeen Malik, the 29-year-old female shooter in the deadly San Bernardino rampage, was a onetime 'modern girl' who became religious during college and then began posting extremist messages on Facebook after arriving in the U.S.,
a family member in Pakistan told the Los Angeles Times." (added emphasis)
So, according to news reports, it wasn't just coming from the unnamed source at Facebook.